Surface tension. Arbitrarily, surface tension refers to the tension
of a liquid/gas interface. Liquids like gases possess kinetic energy, but un-
like gases they have a surface or a boundary layer. This boundary layer
gives a liquid certain properties that gases do not have. Surface tension is
the result of the inherent property of a fluid to tend to form a minimum
surface under all conditions. The minimum surface for a given volume is
in the form of a sphere ; hence, when free to do so liquids assume a spheri-
cal shape. Small drops of water falling on a dusty surface or a waxy leaf
tend to form in drops. Large drops are flattened by gravity. When drops
of water fall on a surface like clean glass, they spread and wetting occurs.
The forces acting between the clean glass and the liquid prevent the liquid
assuming a spherical shape.
The molecules in the interior of a homogeneous liquid do not exhibit any
surface-tension phenomena in relation to one another since they are sub-
jected to a balanced attraction. That is, they are equally attracted by other
molecules on all sides. But the surface film is in a state of tension due to
the unbalanced attractions of the molecules at the surface. The molecules
are attracted only downward and sideways. Whereas the molecules in the
interior of the liquid are evidently arranged at random, those in the surface
are oriented or arranged in a definite and orderly manner. Freundlich
14 RELATION OF COOKERY TO COLLOID CHEMISTRY
states that it is only a step to conceive that this tendency to form a mini-
mum surface resides in a membrane. Kruyt speaks of a boundary layer.
The tension of this membrane is the so-called surface tension of the liquid.
Surface tension is defined by Buchanan and Fulmer as ''the amount of
work required to produce a new surface of unit area at constant tempera-
ture." To enlarge the surface of the liquid requires work. The amount of
work expended to enlarge a surface multiplied by the area increased is
termed free surface energy. The amount of work to enlarge a surface is
greater with increased surface tension. Just as the surface area of a liquid
tends to assume a minimum surface through its inherent surface tension,
so free energy tends to assume a minimum value. The free surface energy
is decreased (1) by reducing the surface area or (2) by reducing the sur-
face tension. Hence, small drops of liquid will unite with large drops if
they are within the same space so that they are connected by their vapor,
thus reducing the surface area.
Water has a high surface tension. Surface tension is measured in dynes
per centimeter. The surface tension of water at 18°C. is 73.0; that of ethyl
alcohol, methyl alcohol, and chloroform at 20°C. is 21.7, 23.0, and 26.7,
respectively. The surface tension of mercury at 15°C. is 436.0. Surface ten-
sion decreases with increase in temperature, becoming zero at the critical
temperature.
Page 14
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Surface tension. Arbitrarily, surface tension refers to the tension
of a liquid/gas interface. Liquids like gases possess kinetic energy, but un-
like gases they have a surface or a boundary layer. This boundary layer
gives a liquid certain properties that gases do not have. Surface tension is
the result of the inherent property of a fluid to tend to form a minimum
surface under all conditions. The minimum surface for a given volume is
in the form of a sphere ; hence, when free to do so liquids assume a spheri-
cal shape. Small drops of water falling on a dusty surface or a waxy leaf
tend to form in drops. Large drops are flattened by gravity. When drops
of water fall on a surface like clean glass, they spread and wetting occurs.
The forces acting between the clean glass and the liquid prevent the liquid
assuming a spherical shape.
The molecules in the interior of a homogeneous liquid do not exhibit any
surface-tension phenomena in relation to one another since they are sub-
jected to a balanced attraction. That is, they are equally attracted by other
molecules on all sides. But the surface film is in a state of tension due to
the unbalanced attractions of the molecules at the surface. The molecules
are attracted only downward and sideways. Whereas the molecules in the
interior of the liquid are evidently arranged at random, those in the surface
are oriented or arranged in a definite and orderly manner. Freundlich
14 RELATION OF COOKERY TO COLLOID CHEMISTRY
states that it is only a step to conceive that this tendency to form a mini-
mum surface resides in a membrane. Kruyt speaks of a boundary layer.
The tension of this membrane is the so-called surface tension of the liquid.
Surface tension is defined by Buchanan and Fulmer as ''the amount of
work required to produce a new surface of unit area at constant tempera-
ture." To enlarge the surface of the liquid requires work. The amount of
work expended to enlarge a surface multiplied by the area increased is
termed free surface energy. The amount of work to enlarge a surface is
greater with increased surface tension. Just as the surface area of a liquid
tends to assume a minimum surface through its inherent surface tension,
so free energy tends to assume a minimum value. The free surface energy
is decreased (1) by reducing the surface area or (2) by reducing the sur-
face tension. Hence, small drops of liquid will unite with large drops if
they are within the same space so that they are connected by their vapor,
thus reducing the surface area.
Water has a high surface tension. Surface tension is measured in dynes
per centimeter. The surface tension of water at 18°C. is 73.0; that of ethyl
alcohol, methyl alcohol, and chloroform at 20°C. is 21.7, 23.0, and 26.7,
respectively. The surface tension of mercury at 15°C. is 436.0. Surface ten-
sion decreases with increase in temperature, becoming zero at the critical
temperature.